1. Field of the Invention
The present invention relates to a rotation sensor adapted to exemplarily detect a rotated angle of a measurement target and a linear displacement corresponding to the rotated angle, and to a displacement detecting apparatus and method utilizing the rotation sensor.
2. Description of the Prior Art
Conventionally, rotation sensors have been utilized to measure a slid amount of an in-vehicle target such as in an in-vehicle power window apparatus and electric power seat apparatus.
As shown in FIG. 1, such a conventional type of rotation sensor 5 comprises: a casing 51 having an opened upper portion; a cover 52 attached onto the opened portion; and a shaft 61 supported at a bottom portion of the casing 51 and at a center portion of the cover 52. The shaft 61 is coupled to a disk-like plate portion 62 within the casing, and this plate portion 62 has a peripheral portion provided with an electroconductive plate 64 of an electrically conductive nature over a certain region of the peripheral portion. Such shaft 61, plate portion 62 and electroconductive plate 64 cooperatively constitute a rotator 60 of the rotation sensor 5.
Meanwhile, arranged inside the rotator 60 is a stator 70. The stator 70 is fixed to the casing via printed board 53 and spacer 54. Further, the stator 70 is constituted of a coil core 73 and an electroconductive plate 74 affixed to a certain region of the circumference of the coil core 73, and the coil core 73 comprises a coil 71 and a bobbin 72. Namely, the electroconductive plate 74 of the stator and the electroconductive plate 64 of the rotator are opposed to each other, in a state for providing a certain gap therebetween. The area to be opposedly and overlappedly defined by the electroconductive plates of the stator 70 and rotator 60 is varied correspondingly to the rotation of the rotator 60.
Clamped between the plate portion 62 of the rotator and the cover 52 is an O-ring 55 which provides a seal such as for avoiding entrance of liquid exemplarily into the coil core 73 and electroconductive plates 64, 74 through the bearing portion for the shaft 61.
Coupled to the end of the shaft protruded from the cover 52 is a pulley 65 wound with a wire 66 made of metal. The wire 66 is pulled (see an arrow A in FIG. 1), correspondingly to a slid amount of a measurement target (not shown in FIG. 1) such as a seat coupled to the wire 66. The pulled wire 66 correspondingly rotates the pulley 65, thereby correspondingly varying that peripheral area of the coil core which is surrounded by both of the electroconductive plate 64 of the rotator and the electroconductive plate 74 of the stator.
Eddy currents to be caused within the electroconductive plates 64, 74 are varied due to the change of the area of the covering region defined by the electroconductive plate 64 of the rotator and the electroconductive plate 74 of the stator, and due to the magnetic flux to be generated by the coil core 73, so that the coil inductance is varied correspondingly to the variation of the eddy currents. Such a variation of the coil inductance is detected by a detecting circuit (not shown), to thereby detect a displacement of the measurement target, such as a slid amount of the seat.
Note, mounted between the pulley 65 and the cover 52 in FIG. 1 is an elastic body 67 for returning the pulley to its origin. Absent the pulling of the wire 66, the pulley 65 and the rotator 60 to be integrally rotated therewith are returned to their origins by virtue of the elastic force of the elastic body itself.
However, there is a gap between the shaft 61 and its bearing portion, in the above type of rotation sensor 5. This leads to an inclination of the shaft 61 as shown in FIG. 2 such as when the shaft 61 is acted by a bending moment from the wire 66 via pulley 65, thereby obstructing a smooth rotation of the rotator 60.
Explaining in detail in this respect, the conventional type of rotation sensor 5 bears the shaft 61 at the positions of the shaft ends in FIG. 2, and these portions of the shaft near the ends of the shaft act as sliding portions of the rotator 60, respectively.
To slide the rotator 60, there is required a certain clearance between the shaft 61 and the bearing portions of the casing. However, excessively large clearances cause the shaft 61 to be inclined relative to the casing 51 as shown in FIG. 2. This inclination leads to failure of parallelism between the sensing portion fixed to the shaft 61 and the coil core 73 (FIG. 1) fixed to the casing 51. This results in fluctuation of a distance between the sensing portion and the coil core 73, thereby fluctuating the output signal, and thereby deteriorating the reliability of the rotation sensor 5.
There is also a problem of interference of the rotation sensor 5 with other parts around it, upon installing the rotation sensor 5.
Concretely, there shall be considered a situation where the rotation sensor 5 is to detect a displacement of a measurement target. This situation provides the above-mentioned structure in which the O-ring 55 for providing the sensor portion with a waterproof function is arranged between the rotator 60 and the casing 51, and the wire 66 is wound around the pulley 65, while the other end of the wire 66 is coupled to the detection target. The displaced portion fixed to the wire as well as the wire itself are exposed to the exterior of the casing of the rotation sensor 5, and also the pulley 65 wound with such a wire 66 is exposed to the exterior of the casing of the rotation sensor 5. This requires to endeavor to keep the pulley 65 from interfering with other parts, such as upon mounting the rotation sensor 5 onto a vehicular body, thereby resulting in a troublesome operation. Although it is conceivable to adopt a structure for additionally providing a specific protection wall outside the pulley 65 to thereby avoid the aforementioned interference with other parts, this leads to an increased number of parts and an increased cost.
Further, when the rotation sensor 5 is utilized to exemplarily detect a seat slid amount of a vehicle, there is caused an additional problem that the rotator 60 is not smoothly rotated such as due to vibrations during running of the vehicle.